The present invention relates to carbon black pellets and, more particularly, to carbon black pellets exhibiting good handling characteristics, attrition resistance, and good dispersibility when incorporated in polymeric or elastomeric media.
Various treatment methods to improve the bulk handling, dispersibility, and attrition resistance of carbon blacks include wet pelletizing and dry pelletizing techniques. According to such techniques, a carbon black, for example, a fluffy carbon black, is treated with one or more binding agents and then pelletized to form carbon black pellets. Among the various binders used in forming carbon black pellets, wax and other organic components have been utilized. U.S. Pat. No. 5,654,357 to Menashi et al., which is incorporated herein in its entirety by reference, teaches using an organic compound or mixture of organic compounds having certain properties such that, when used to pelletize carbon black have resulted in attrition-resistant carbon black pellets exhibiting good dispersibility in polymeric and elastomeric media.
U.S. Pat. No. 3,353,974 describes mixing carbon black with a wax to form a plastic mix that is then extruded at elevated temperatures. A pigment to matrix weight ratio range of from 10:90 to 90:10 is mentioned.
U.S. Pat. No. 3,429,958 describes producing pelletized carbon black by mixing carbon black with a molten wax in a pin pelletizer. For furnace blacks, the weight ratio of carbon black to wax, recited in this patent, is from 50:50 to 30:70, thus requiring high wax levels.
U.S. Pat. No. 4,230,501 describes mixtures of carbon black with a combination of waxy materials and wax-like materials such as polyethylene glycol or hydrocarbon resins. A variety of mixtures are described at temperatures in excess of the melting point of the wax or wax-like materials. The patent describes compositions containing 51% by weight to 85% by weight pigment that can be easily dispersed and let down directly into thermoset and thermoplastic resins.
U.S. Pat. No. 4,285,994 describes free-flowing pigments produced by tumbling together a finely divided wax with a powdered pigment. The tumbling process, when conducted at ambient temperatures, reportedly results in the coating of the wax particles by the pigment. When conducted at elevated temperatures, the pigment absorbed the wax. The pigment contents of the resulting products are reported as ranging from 70% by weight to 95% by weight.
U.S. Pat. No. 4,310,483 describes mixtures of carbon black with pentaerythritol tetrastearate (PETS) that are then pelletized in a tilting pan granulator at 100° C. The patent describes a composition containing a ratio of from 2 parts by weight to 50 parts by weight granulating auxiliary to 100 parts by weight additive (pigment).
U.S. Pat. No. 4,484,952 describes carbon black dispersed in a molten organic carrier consisting of a mono or tetraester of pentaerythritol and stearic acid, stearylamide, ethylene bisstearylamide or hydrogenated castor oil. The resulting dispersion is then prilled (i.e., sprayed) to form free flowing pellets. The patent describes resulting products containing from 15% by weight to 95% by weight pigment.
U.S. Pat. No. 4,569,834 describes the use of an aqueous emulsion of wax to pelletize carbon black in a pin pelletizer. Waxes described in the patent as suitable are substituted and unsubstituted polyalkene waxes with a most preferred additive being a surface oxidized polyethylene having a molecular weight of from 1800 to about 5000. The patent reports resulting pelletized products exhibited enhanced dispersibility characteristics. The patent also reports that the amount of aqueous emulsion used should be sufficient to provide from 1 to 10 parts by weight oxidized polyethylene per 100 parts by weight of dry carbon black pellets.
All patents, patent applications, and publications mentioned throughout this application are incorporated in their entirety herein by reference.
A need exists for producing carbon black pellets that are attrition resistant, exhibit good handling and dispersibility properties, and use lower levels of wax or organic compound.
It is desirable to provide carbon black pellets having even better attrition resistance, handling properties, and dispersibility than carbon black pellets currently available.
It is also desirable to provide coated carbon black pellets with properties that improve and enhance the production of rubbers that are formed from the coated carbon black pellets.
It is also desirable to provide coated carbon black pellets that offer improved viscosity properties, which improves flow characteristics and reduces mold fouling.